Internet giant Google has extended its Google Trends service, originally launched in 2006, including specific websites in its analytical tool developed by Google Labs. The new function displays specific traffic information on a certain site. It sound great, indeed, and puts the search leader in direct competition with similar services by Alexa, Comscore and others. But how accurate are they?

Only the website owners and Google know that. The new service, as its rivals, do not actually measure traffic, they estimate it through a variety of powerful algorithms. The problem is that Google still does not give website owners the option of contributing their highly accurate Google Analytics information, which relies on actual traffic measured by special scripts installed on the site.

Only aggregated opt-in anonymous Google Analytics data, opt-in consumer panel data, search data and other data mined from third-party market research is entered into Google Trends' algorithms which then estimate as accurately as possible given these limitations traffic on the selected website.

Meanwhile, Mozilla is developing what might be a revolutionary, highly accurate way of estimating website traffic. The company wants to harvest its nearly 20 percent market share in browser usage to give its users the option of contributing automatically to a traffic measuring system.

Of course, Google could always tap into their Analytics database and bury other traffic ranking systems, but strangely it was reluctant to do so, even on an opt-in system. Its Google Trends tool has recently gained momentum, after being apparently abandoned for months at a time in 2006 and 2007. As part of its coming back, Google launched Google Hot Trends, which displays the top 100 hot searches of the past hour, whereas Google its parent shows the most popularly searched terms for a period of time between 2004 and present.